Microwave applicator

ABSTRACT

A microwave applicator having a probe which comprises an elongate shaft ( 14 ), the shaft having an external tubular wall ( 18 ), a radiating portion ( 15 ) disposed at the distal end of the shaft ( 14 ), a transmission line ( 17 ) extending to the radiating portion internally of the tubular external wall ( 18 ), and an elongate flow dividing member ( 19 ) which co-extends with the transmission line ( 17 ) longitudinally of the shaft ( 14 ), the side wall of the transmission line ( 17 ) and the side wall of the flow dividing member ( 19 ) contacting each other and contacting the internal surface of the external tubular wall ( 18 ) at two-spatially separated discrete positions, thereby defining a pair of flow channels ( 20, 21 ) inside the shaft ( 14 ). In use, cooling fluid can pass down one channel ( 20 ) and return via the other channel ( 21 ). The structure of the probe is uncomplicated and the probe is straightforward to assemble.

This invention relates to a microwave applicator for medical use.

It's well known to ablate body tissue using a microwave applicator whichheats and destroys the surrounding tissue. One use of such an applicatoris in the non-invasive treatment of cancer in an internal body organsuch as the liver. GB2415630 discloses an applicator of theabove-mentioned type comprising a probe having a thin elongate shaft,which can be inserted into the patient. The proximal end of the probecomprises a handle which is connected to an external microwave generatorby an elongate flexible cable. A thin elongate microwave transmissionline extends inside the probe from the handle to a radiating tipdisposed at or adjacent the distal end of the probe. In use, themicrowave field radiated from the tip heats and ablates the surroundingtissue in a localised area.

A disadvantage of the above-mentioned applicator is that the probe canheat up for a variety of reasons. Firstly, power losses can occur in thetransmission line extending along the probe to the tip, which powerlosses heat the transmission line and the surrounding parts of theprobe. Secondly, the radiated microwave energy can heat the probe.Thirdly, the heat from the ablation can be conducted back along theprobe. Such heating of the probe is undesirable, since it can burn thepatient's skin at the point of entry of the probe or it can burn otherparts of the patient's body adjacent the shaft of the probe. Indeed, UKgovernment regulations specify that no external part of any medicalapparatus should exceed 48° in temperature.

In order to overcome the above-mentioned problems, it is well known topass a liquid, such as a saline solution, along the probe so as to coolthe probe. In use, the liquid passes out of the apertures in the distalend of the probe into the surrounding body cavity. A disadvantage ofthis arrangement is that the liquid fills the wound and undesirablyeither flows out of or into the body. Furthermore, the radiatedmicrowave energy can heat the liquid in the body cavity.

In order to overcome the above-mentioned problems, WO2005/011049,DE2407559 and U.S. Pat. No. 4,375,220 each disclose microwaveapplicators in which cooling fluid is passed along the probe to itsdistal end along one flow passage and then returned along another flowpassage.

In order to achieve this, each of the above-mentioned applicatorscomprise a complicated arrangement of cooling pipes or formers insidethe probe, which define the flow and return passages. It will beappreciated that microwave applicator probes are advantageously thin, inorder to enable them to be used as non-invasively as possible. However,a disadvantage of the pipes and formers used in the above-mentionedapplicators is that the flow and return passages need to be relativelylarge in order to achieve the desired flow rates and it will beappreciated that this correspondingly increases the overall diameter ofthe probe. Furthermore, the probe also needs to be of a relatively largediameter in order to facilitate the insertion of the pipes or former.

We have now devised a microwave applicator which alleviates theabove-mentioned problems.

In accordance with the present invention, there is provided a microwaveapplicator having a probe which comprises an elongate shaft, the shafthaving an external tubular wall, a microwave radiating portion disposedat the distal end of the shaft and a transmission line extending to saidradiating portion internally of said tubular external wall, wherein anelongate flow dividing means extends internally along said tubularexternal wall and sealingly contacts the internal surface of saidtubular wall along its length at two-spatially separated discretepositions around its periphery, the periphery of said flow dividingmeans being out of contact with said tubular wall between said twopositions to define first and second discrete flow passages which extendlongitudinally of said shaft for carrying cooling fluid.

In use, cooling fluid can be passed along the first passage to cool theprobe, the cooling fluid then returning along the second passage. Sincethe flow dividing means and external tubular wall together define theflow passages, the need for complicated pipes and formers is avoided andhence the diameter of the probe can be minimised. The flow dividingmeans is also relatively straightforward to insert into the probe, aswill be explained hereinafter.

In one embodiment, the flow dividing means comprises a single flowdividing member having an external cross-sectional shape which isdifferent from the internal cross-sectional shape of the externaltubular wall. For instance, the external cross-sectional shape of theflow dividing means may be circular and the internal cross-sectionalshape of the tubular wall may be oval or vice-versa.

Said flow dividing member may comprise a hollow tube carrying saidtransmission line or the transmission line may itself form said flowdividing member.

In an alternative embodiment, said flow dividing means comprises saidtransmission line and an elongate flow dividing member which co-extendswith said transmission line longitudinally of said shaft, the side wallof the transmission line and the side wall of the flow dividing membercontacting each other and contacting said internal surface of theexternal tubular wall at said two-spatially separated discretepositions.

Said flow dividing member can be relatively thin and preferably has adiameter substantially equal to or greater than the difference betweenthe internal diameter of said tubular external wall of the shaft and theexternal diameter of said transmission line.

It is often desirable to be able to sense a parameter such astemperature at the radiating tip. In order to achieve this, said flowdividing member may comprise a tube or a cable carrying one or morewires to the distal end of the shaft. In use the wire(s) may carry ameasuring signal from a sensor at the distal end of the shaft.

The transmission line preferably comprises a conductor which is alsoconnected to the sensor and forms a signal pair with the wire of theflow dividing member.

Preferably, said flow dividing member comprises a tube or a cablecarrying at least one wire of a thermocouple, said one wire preferablybeing formed of a first metal such as constantan. The distal end of thewire of said first metal is preferably connected at its distal end tosaid conductor of the transmission line, the conductor being formed of asecond metal such as copper. Preferably, a body of said second metal isdeposited on the distal end of the wire of said first metal in order toform a reliable junction between said metals. The body of second metalis preferably held in electrical contact with said conductor of thetransmission line within the probe.

Said flow passages preferably have substantially equal cross-sectionalareas, the combined cross-sectional areas of the flow passagespreferably being equal to the internal cross-sectional area of thetubular external wall minus the cross-sectional area of the transmissionline minus the cross-sectional area of the flow dividing member.

Preferably the distal end of the flow dividing means terminates prior tosaid radiating portion of the probe, in order to form a cross-overbetween said flow passages.

Preferably at least one of said flow passages is closed at the proximalend of the probe by a seal or other member.

Preferably the proximal end of the shaft extends into a manifold, whichpreferably forms a handle of the probe.

Preferably the manifold comprises first and second compartments whichare sealingly separated from each other, said first and second flowpassages respectively communicating with said first and secondcompartments. Preferably the first and second compartments of themanifold are arranged at respective positions longitudinally of the axisof the shaft.

Preferably an aperture is formed in the tubular external wall of theshaft at the proximal end thereof, wherein said aperture connects a saidflow passage with a said compartment of the manifold.

Preferably one of the chambers of the manifold comprises a port forconnecting to an external flow duct carrying cooling fluid. This flowduct preferably carries cooling fluid into the probe from a pump orother pressurised source of cooling fluid.

Preferably the other chamber of the manifold comprises a port whichconnects to the distal end of an elongate flexible cable of theapplicator, which cable extends from a source of microwave radiation,said cable comprising a flow duct for carrying said cooling fluid. Theflow duct of the cable preferably carries cooling fluid out of the probeto a drain or a collection vessel. The flow of fluid along the cablethus further serves to cool the cable, which can become hot due to powerlosses.

Preferably the proximal end of the cable comprises a port which acts asan inlet or outlet of the flow duct of the cable.

Also in accordance with the present invention, there is provided amethod of forming a microwave applicator probe comprising providing anelongate tube, deforming the tube perpendicular to its longitudinalaxis, inserting elongate flow dividing means into the deformed tube andreleasing the tube to allow the tube to recover its shape.

The deformation of the tube allows the elongate fluid dividing means tobe easily inserted into the tube. Once released, the tube recovers itsshape and compresses the elongate flow dividing means into a positionwhere it contacts the internal surface of the wall at two spatiallyseparated positions around the periphery thereof. In this manner, twosealingly-separated flow passages are formed along the tube.

Preferably the method comprises inserting an elongate transmission lineinto the tube. The elongate transmission line may form said flowdividing means either alone or in conjunction with an elongateflow-dividing member. In the latter case, the transmission line and theflow dividing member may be inserted into the tube simultaneously or oneafter the other. In the latter case, one of the members may be insertedinto the tube prior to the deformation thereof.

Embodiments of the present invention will now be described by way ofexamples only and with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of a first embodiment of microwave applicatorin accordance with the present invention;

FIG. 2 is a perspective outline view of the distal end of a probe of theapplicator of FIG. 1;

FIG. 3 is a perspective outline view of the proximal end of a shaft ofthe probe of the applicator of FIG. 1;

FIG. 4 is a perspective outline view of the proximal end of the probeand a microwave feed cable of the applicator of FIG. 1;

FIG. 5 is a perspective outline view of a portion of a manifold of theprobe of the apparatus of FIG. 1;

FIG. 6 is a perspective outline view of an outlet chamber of the feedcable of the applicator of FIG. 1;

FIG. 7 is a perspective schematic view illustrating the method ofmanufacture of the shaft of the probe of the applicator of FIG. 1;

FIG. 8 is a longitudinal sectional view through the shaft of a probe ofa second embodiment of microwave applicator probe in accordance with thepresent invention;

FIG. 9 is a sectional view along the line IX-IX of FIG. 8; and

FIG. 10 is a transverse sectional view through the shaft of a probe of athird embodiment of microwave applicator probe in accordance with thepresent invention.

Referring to FIG. 1 of the drawings, there is shown a microwaveapplicator probe comprising a microwave generator 10 connected to anapplicator probe 11 via an elongate flexible feed cable 12. The probe 11comprises a handle portion 13 and an elongate shaft portion 14 extendingfrom the handle 13. In use, the generator 10 generates a microwavesignal which is transmitted along the feed cable 12 to the probe 11. Themicrowave signal is then transmitted along the shaft 14 of the probe toa radiating tip 15 at the distal end thereof.

Referring to FIG. 2 of the drawings, the shaft 14 comprises an externalelongate tubular wall 14 formed of stainless steel. A co-axialtransmission line 17 extends internally of the tubular wall 14, thetransmission line 17 being coupled at its proximal end to the microwavefeed cable 12 and at its distal end to a radiating antenna 16 disposedinside the tip 15 of the probe 11. An elongate flow dividing member 19,in the form of a solid cable or wire, co-extends with the co-axialtransmission line 17 along a substantial part of the length thereof, themember 19 terminating a short distance away from the radiating antenna16.

The combined diameter of the transmission line 17 and the flow dividingmember 19 is slightly greater than the internal diameter of the tubularexternal wall 18, such that the transmission line 17 and flow dividingmember both positively contact the internal surface of the externaltubular wall 18 and each other along a substantial part of the length ofthe shaft 14. The transmission line 17 and flow dividing member 19 thustogether define two flow channels 20, 21, which extend longitudinally ofthe shaft 14 from the proximal end to the point at which the flowdividing member 19 terminates. The two flow channels 20, 21 areinterconnected beyond the point at which the flow dividing member 19terminates.

Referring to FIGS. 3 and 4 of the drawings, one of the channels 20 issealed by a member 22 at the proximal end of the shaft 14. A pluralityof apertures 27 are formed in the external tubular wall 18 of the shaft14 at the proximal end thereof, the apertures 27 communicating with thesealed channel 20. The proximal end of the shaft 14 extends into amanifold 23 disposed inside the handle 13 of the probe 11. The manifold23 is generally cylindrical and is divided into two axially-disposedchambers 24, 25 by a boundary wall 26 which extends normal to thelongitudinal axis of the shaft 14. The proximal end of the shaft 14extends into the manifold 23 and through the boundary wall 26, such thatthe apertures 27 open into the distal chamber 24 of the manifold 23, thesecond (un-sealed) flow channel 21 of the shaft 14 opening into theproximal chamber 25 of the manifold 23. An inlet port 28 extendsradially outwardly from the side wall of the manifold 23, the inlet port28 communicating with the distal chamber 24 of the manifold 23.

The proximal end wall 13 of the manifold 23 is connected to the feedcable 12, the feed cable 12 comprising an outer tube 28 and a co-axialcable 29 extending loosely inside the tube 28. The co-axial cable 29extends through the proximal end wall 30 of the manifold 23 and isconnected inside the chamber 25 to the co-axial transmission line 17 bya co-axial coupling 31. The distal end of the tube 28 is sealinglycoupled to an aperture in the proximal end wall 30 of the manifold 23,such that the interior of the tube 28 opens into the proximal chamber 25of the manifold 23.

Referring to FIG. 6 of the drawings, the proximal end of the feed cable12 is connected to an elongate cylindrical outlet chamber 32. Theproximal end of the tube 28 of the feed cable 12 is coupled to theoutlet chamber 32, such that the interior of the tube 28 opens into theoutlet chamber 32. The co-axial cable 29 extends through the outletchamber 32 to a co-axial connector 34 on the external face of theproximal end wall of the chamber 32. An outlet port 32 extends radiallyoutwardly from the side wall of the outlet chamber 32.

In use, the co-axial connector 34 is connected to the microwavegenerator 10. The inlet port 28 of the manifold 23 is connected to apump via an elongate tube (not shown). The outlet port 33 is connectedto a collection vessel via an elongate tube (not shown). When energised,the pump pumps cooling fluid into the distal chamber 24 of the manifold23 through the inlet port 28. The cooling fluid then flows through theapertures 27 in the external tubular wall 18 of the shaft 14 and intothe flow channel 20. The cooling fluid then flows longitudinally of theshaft 14, thereby cooling the external wall 18 of the shaft and thetransmission line 17. The cooling fluid then crosses from the flowchannel 20 to the other flow channel 21 at the distal end of the shaft14, beyond the point at which the flow dividing member 19 terminates.The cooling fluid then returns along the shaft 14 via the coolingchannel 21, whereupon it flows into the proximal chamber 25 of themanifold 23. The fluid then flows out of the manifold 23 and into thefeed cable 12, whereupon it flows along the cable 12 in an annular flowchannel defined between the outer tube 28 and the co-axial cable 29. Thefluid then flows out of the outlet chamber 32 through the outlet port 33to a collection vessel. In this manner, the cooling fluid also cools theco-axial cable 29.

Referring to FIG. 7 of the drawings, the co-axial transmission line 17and the flow dividing member 19 are inserted into the external tubularwall 18 of the shaft 14 by compressing the external tubular wall 18transverse its longitudinal axis into an oval shape. The transmissionline 17 and the flow dividing member 19 can then be easily inserted intothe deformed external tubular wall 18. Once inserted, the applied forcecan be removed, thereby allowing the external tubular wall 18 to recoverits shape, such that the co-axial transmission line 17 and the flowdividing member 19 become compressed against each other and against theexternal tubular wall 18.

Referring to FIGS. 8 and 9 of the drawings, there is shown analternative embodiment of microwave applicator probe which is similar tothe probe of FIGS. 1-7 and like parts are have given like referencenumerals. In this embodiment, the elongate flow dividing member 19 isreplaced by a thin tube, e.g formed of stainless steel. An elongateinsulated wire 36 of constantan extends from a measuring instrument 43through the tube 35. The insulation is removed from the distal end ofthe constantan wire and a body 37 of copper material is deposited ontothe exposed conductor of the constantan wire 36. The transmission line17 comprises an outer copper sleeve 40. An elongate central conductor 38extends inside the copper sleeve 40 and is insulated therefrom by adielectric sleeve 39. The body 37 of copper on the constantan wire 36makes contact with the copper sleeve 40 of the transmission line 17. Thebody 37 of copper has a diameter which is substantially equal to thediameter of the tube 35, such that it is held tightly in contact withthe copper sleeve 40 of the transmission line 17. The external surfaceof the copper body 37 may be electro-plated to ensure a reliable contactwith the copper sleeve 40 of the transmission line 17. The proximal endof the copper conductor 40 is connected via a wire 42 to the measuringinstrument 43. The tube 35 is preferably sealed by the constantan wire36 or another member against fluid flow. In this way, the risk of fluidusing the tube 35 as a return path is avoided.

It will be appreciated that a complete circuit from the thermocoupleinstrument 43 is thus created by the constantan wire 36, the copper body37 and the copper sleeve 40 of the transmission line 17. Thecopper-constantan junction inside the body 37 forms a thermocouplejunction which can be used to provide an indication of the temperatureat the tip of the probe 11.

The two thermocouple wires 36,42 extending from the measuring instrument43 preferably extend into the outlet manifold 32 and along the cable 12in the annular flow channel defined between the outer tube 28 and theco-axial cable 29. The wires 36,42 then extend through the manifold 13to the shaft 14 of the probe 11. This arrangement helps to hide thewires 36,42 and improves the overall appearance of the applicator.

Referring to FIG. 10 of the drawings, there is shown an alternativeembodiment of microwave applicator probe, which is similar to theembodiment of FIGS. 8 and 9 and like parts are given like referencenumerals. In this embodiment, the separate flow-dividing member 19 isomitted and instead, the transmission line 17 acts on its own to definetwo flow-channels 120, 121. This is achieved by providing the shaft 14with an external tubular wall 118 which is normally oval in section. Thetransmission line 17 is inserted into the external wall 118 by deformingthe wall transverse its longitudinal axis until it comes generallycircular in shape: this allows the transmission line 17 to be inserted,whereupon the deforming force can be removed such that the transmissionline 17 contacts the external wall 118 at diametrically opposedpositions.

A microwave applicator probe in accordance with the present invention isrelatively simple and inexpensive in construction, yet enables the probeto be reliably cooled.

The invention claimed is:
 1. A microwave applicator comprising: anelongated shaft having an external tubular wall; a microwave radiatingportion near a distal end of the shaft; a flow dividing elementcomprising of a transmission line and a flow dividing member, thetransmission line extending to the microwave radiating portion, thetransmission line and flow dividing member extend longitudinally alongthe shaft, a first side of the transmission line outer wall and a firstside of the flow dividing member outer wall contacting each other, asecond side of the transmission line outer wall and a second side of theflow dividing member outer wall contacting the internal surface of theexternal tubular wall at two-spatially separated locations to define afirst flow passage and a second flow passage which extend longitudinallyalong the shaft.
 2. A microwave applicator as claimed in claim 1, inwhich the external cross-sectional shape of the flow dividing member iscircular and the internal cross-sectional shape of the tubular wall isoval or vice-versa.
 3. A microwave applicator as claimed in claim 1, inwhich said flow dividing member comprises a hollow tube.
 4. A microwaveapplicator as claimed in claim 1, in which said flow dividing member isformed by a solid cable or wire.
 5. A microwave applicator as claimed inclaim 1, in which said flow dividing member has a diameter equal to orgreater than the difference between the internal diameter of saidtubular external wall of the shaft and the external diameter of saidtransmission line.
 6. A microwave applicator as claimed in claim 1, inwhich said flow passages have substantially equal cross-sectional areas,the combined cross-sectional areas of the flow passages being equal tothe internal cross-sectional area of the tubular external wall minus thecross-sectional area of the transmission line minus the cross-sectionalarea of the flow dividing member.
 7. A microwave applicator as claimedin claim 1, in which the distal end of the flow dividing elementterminates prior to said radiating portion of the applicator, in orderto form a cross-over between said flow passages.
 8. A microwaveapplicator as claimed in claim 1, in which at least one of said flowpassages is closed at the proximal end of the applicator by a seal.
 9. Amicrowave applicator as claimed in claim 1, in which the proximal end ofthe shall extends into a manifold.
 10. A microwave applicator as claimedin claim 9, comprising a handle at the proximal end of the shaft whichcomprises said manifold.
 11. A microwave applicator as claimed in claim9, in which the manifold comprises first and second compartments whichare sealingly separated from each other, said first and second flowpassages respectively communicating with said first and secondcompartments.
 12. A microwave applicator as claimed in claim 11, inwhich the first and second compartments of the manifold are arranged atrespective positions longitudinally of the axis of the shaft.
 13. Amicrowave applicator as claimed in claim 11, in which an aperture isformed in the tubular external wall of the shaft at the proximal endthereof, wherein said aperture connects a said flow passage with a saidcompartment of the manifold.
 14. A microwave applicator as claimed inclaim 11, in which one of the chambers of the manifold comprises a portfor connecting to an external flow duct carrying cooling fluid.
 15. Amicrowave applicator as claimed in claim 14, in which said flow ductcarries cooling fluid into the applicator from a pump or otherpressurized source of coo ling fluid.
 16. A microwave applicator asclaimed in claim 14, in which the other chamber of the manifoldcomprises a port which connects to the distal end of an elongateflexible cable of the applicator, which cable extends from a source ofmicrowave radiation, said cable comprising a flow duct for carrying saidcooling fluid.
 17. A microwave applicator as claimed in claim 16, inwhich the flow duct of the cable carries cooling fluid out of theapplicator to a drain or a collection vessel.
 18. A microwave applicatoras claimed in claim 16, in which the proximal end of the cable comprisesa port which acts as an inlet or outlet of the flow duct oft cable. 19.A microwave applicator as claimed in claim 16, in which the proximal endof the shaft comprises a fluid inlet and a fluid outlet respectivelyconnected to said first and second passages.
 20. A microwave applicatoras claimed in claim 1, comprising means for creating a fluid flowthrough the applicator such that fluid flows along said first passagetowards the distal end of the shaft and returns along said secondpassage.
 21. The microwave applicator as claimed in claim 1, wherein theflow dividing member having an outer diameter, the transmission linehaving an outer diameter, the external tubular wall having an innerdiameter, the combination of the flow dividing member outer diameter andtransmission line outer diameter creates an interference fit with theinternal diameter of the external tubular wall.